1. Field of the Invention
The present invention relates to a burn-in apparatus to perform a burn-in test for semiconductor integrated circuit devices.
2. Description of the Background Art
The burn-in test is performed in a checking process of semiconductor integrated circuit devices. An object of the burn-in test is to remove semiconductor integrated circuit devices of potential early defect from mass-produced semiconductor integrated circuit devices prior to shipping.
FIG. 4 is a schematic block diagram showing a configuration of a conventional burn-in apparatus.
Referring to FIG. 4, the burn-in apparatus 100 includes a body 10 and a burn-in board 11. Body 10 includes a device power supply generation circuit 12. Device power supply generation circuit 12 supplies set voltage Vs to burn-in board 11 during the burn-in test. Set voltage Vs will be described below. Burn-in board 11 mounts a plurality of semiconductor integrated circuit devices to be checked DUTs (devices under test) (a semiconductor integrated circuit device is referred to as a checked device hereinafter). Each of a plurality of checked devices DUTs is connected to device power supply generation circuit 12 via a protective resistance element R1.
If any of a plurality of checked devices DUTs were broken during the burn-in test, protective resistance element R1 prevents the broken checked devices DUTs from affecting voltage applied to other cheched devices DUTs.
Therefore, when burn-in apparatus 100 applies test voltage V to each of a plurality of checked devices DUTs, the set voltage Vs output from device power supply generation circuit 12 is set as follows, considering voltage drop due to protective resistance element R1;
Vs=V+iR;
wherein i is a value of current consumption of each checked device DUT and R is a resistance value of protective resistance element R1.
The value of current consumption of checked device i would be different, however, depending on types of semiconductor integrated circuit devices as checked devices DUTs, or on test conditions such as test rate during the burn-in test. As the result, set voltage Vs had to be set for every type of checked device and every test condition.
In conventional burn-in apparatus 100, set voltage Vs was set manually. Thus, the frequent settings of set voltage Vs made the work load heavier.
The value of current consumption of each checked device i would also be different because of variations in manufacturing of respective checked devices DUTs. Therefore, the work load became heavier to improve accuracy of test voltage V.
An object of the present invention is to provide a burn-in apparatus of which test voltage applied to checked devices can be set easily with high accuracy.
A burn-in apparatus according to the present invention includes a burn-in board, a device power supply generation circuit, an average voltage calculating circuit, and a voltage correction circuit. The burn-in board mounts a plurality of checked devices. The device power supply generation circuit supplies test voltage for a burn-in test to a plurality of checked devices mounted on the burn-in board. The average voltage calculating circuit measures the test voltage supplied to each checked device and outputs the average voltage. The voltage correction circuit outputs a control signal to control the device power supply generation circuit in accordance with the average voltage.
Thus the burn-in apparatus can set the test voltage in accordance with the average voltage calculated in the average voltage calculating circuit.
The voltage correction circuit preferably includes a comparator. The comparator receives the average voltage and a predetermined voltage and outputs the control signal.
Thus the burn-in apparatus compares the average voltage with the predetermined voltage and controls the device power supply generation circuit with this result. This can improve the accuracy of test voltage output from the device power supply generation circuit.
Furthermore, the burn-in apparatus preferably includes a sensing circuit which senses a plurality of checked devices mounted on the burn-in board, and the average voltage calculating circuit measures the test voltage supplied to each checked device sensed by the sensing circuit and outputs the average voltage.
Therefore the burn-in apparatus can measure the test voltage for the checked devices mounted on the burn-in board. Consequently, the accuracy of set test voltage is improved.
Furthermore, the sensing circuit preferably senses two or more operable checked devices among a plurality of checked devices.
Therefore the burn-in apparatus can sense the checked devices which are mounted on the burn-in board and are not broken by the test. Consequently, more accurate test voltage can be set.
It is preferred that the sensing circuit includes a function testing circuit to perform a function test for a plurality of checked devices, and the average voltage calculating circuit outputs average voltage in accordance with the result of the function test.
Therefore the burn-in apparatus can sense the checked devices mounted on the burn-in board by the function test.
The average voltage calculating circuit preferably measures the test voltage supplied to each of two or more checked devices among a plurality of checked devices and outputs the average voltage.
Therefore the burn-in apparatus can reduce the area required for wiring to measure the test voltage.
The burn-in apparatus according to the present invention measures for every checked device the test voltage applied to the checked devices and calculates the average voltage. The burn-in apparatus also corrects the test voltage using the calculated average voltage. Consequently, the burn-in apparatus can set the power supply voltage applied to the checked devices readily with high accuracy.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.